CSIRO PUBLISHING www.publish.csiro.au/journals/is Invertebrate Systematics, 2007, 21,311—339 Systematics, phylogeny and historical biogeography of the Pentagonaster clade (Asteroidea: Valvatida: Goniasteridae) Christopher Mah Department of Invertebrate Zoology, National Museum of Natural History, MRC-1 63, PO Box 3701 2 Smithsonian Institution, Washington, DC 20560, USA. Email:
[email protected] Abstract. Morphology-based phylogenetic hypotheses developed for living and fossil goniasterid asteroids have pro- vided several unique opportunities to study bathymetric and biogeographic shifts for an ecologically important group of prominent, megafaunal invertebrates. A cladistic analysis of 18 ingroup taxa employing 65 morphological characters resulted in a single most parsimonious tree. The tree supports assignment of the Atlantic Tosia parva (Perrier, 1881) and the Pacific Tosia queenslandensis Livingstone, 1932 to new, separate genera. The phylogenetic tree supports offshore to onshore bathymetric shifts between basal and derived taxa. The phylogeny is also consistent with historical events sur- rounding the separation of Antarctica from Australia and South Africa. Buterminaster Blake & Zinsmeister, 1988 from the Eocene La Meseta Formation, Antarctic Peninsula, was included in the phylogenetic analysis and is now supported as the only fossil species in the genus Pentagonaster Gray, 1840. Pentagonaster stibarus H. L. Clark, 1914 is separated from syn- onymy with P. dubeni Gray, 1847 and resurrected as a valid species. The new genus, Akelbaster, gen. nov, shows unusual new structures that resemble cribiform organs, although their function has not been determined. One specific ingroup lineage, including Tosia and Pentagonaster, attains a much larger adult size than those of its sister-taxa, suggesting that Cope's rule may apply to asteroids within this clade.